This application claims the priority of Application No. 2001-345505, filed Nov. 12, 2001, in, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a fuel pump for supplying fuel in an internal combustion engine and a direct fuel injection engine, and particularly to a fuel pump used for a high pressure pump of a fuel injector for a direct fuel injection engine of a vehicle in which fuel is directly injected into a combustion chamber from the fuel injector attached to the combustion chamber of the vehicle engine, and to the direct fuel injection engine.
In general, an in-cylinder direct fuel injection device requires a high pressure pump capable of supplying gasoline into cylinders of an internal combustion engine with a high pressure above 3 MPa because it is necessary to directly inject gasoline into the cylinders even at the compression stroke.
One type of the high pressure pumps is a radial plunger high pressure fuel pump. A high pressure fuel pump of this type is disclosed, for example, in Japanese Patent Application Laid-Open No. 10-318091.
Another type of the high pressure pump is a slant-plate axial plunger pump in which a rotating motion of a slant plate rotated by a shaft inside a housing is converted to an oscillating motion by an oscillating plate, and fluid is sucked and pressurized to be delivered at a high pressure by a plunger reciprocally moved by the oscillating motion of the oscillating plate. The slant-plate axial plunger pump is disclosed, for example, in Japanese Patent Application Laid-Open No. 9-236080.
In the fuel pumps having these structures, fuel is sucked and delivered by the motion of a reciprocally moving piston or pistons inside a fuel chamber of a mechanism portion generating a high pressure, and thereby the fuel is pressurized to a high pressure. Accordingly, fluid existing in the fuel chamber is only the fuel of gasoline. Therefore, the gasoline acts as a lubricating oil at a sliding portion in each mechanism. Further, at a potion other than the fuel chamber, sliding in various kinds of the mechanisms converting the rotating motion to the reciprocal motion is performed using a lubricating oil under condition of a high speed (high peripheral speed) and high surface pressing pressure.
As for the wear-resistant sliding members, Japanese Patent Application Laid-Open No. 7-216548 discloses, for example, a wear-resistant sliding member of a fuel injection nozzle device in which a nitride film is formed by plasma nitriding treatment at a portion in the fuel injection nozzle relatively contacting to or sliding on another member, and a TiCN film is further formed by plasma CVD on the nitride film.
The surface treated layer of the prior art will be described below. It is described that a method of forming the film is plasma CVD, and the material of the hard film is a TiCN film. Further, in regard to thickness of the surface treated layer, the nitride film is 5 to 20 μm thickness, and the TiCN is 2 to 10 μm thickness. Accordingly, the range of the thickness of the surface treated layer becomes 7 μm at minimum and 30 μm at maximum. Since the film is generally formed under a pressure of several Pa by the plasma CVD, the plasma CVD method is better than the PVD method in treatment of a narrow portion due to the mean free path (traveling distance of a particle in a gas atmosphere without collision), but the difficulty of treatment is nearly equal to each other. On the other hand, since chlorine of a component of a feed gas is mixed into the film, there is a problem in that the film properties such as corrosion resistance, wear resistance, hardness and the like are degraded.
The TiCN film has a property of combining the properties of TiN and TiC which compensate individual problems each other. The hardness of the film is within a range of Hv 2500 to 3000, but the friction coefficient is generally as high as 0.6. On the other hand, the friction coefficient of carbon group films (DLC) is a very low value below 0.1. Forming of the nitride film {circle around (1)} makes the surface roughness of the TiCN film fine. It is described that a purpose of increasing the hardness of the base material is {circle around (2)} to improve the ability of preventing the TiCN film from peeling. However, it is not described on the reason why the thickness of the TiCN film is set to 5 to 20 μm. It is described that the effect of the TiCN film as a wear resistant film is insufficient when the thickness is thinner than 2 μm, and a bad influence due to internal stress of the TiCN film occurs when the thickness is thicker than 10 μm. On the other hand, the carbon group film (DLC) has an excellent wear resistance even when the thickness is 0.5 to 1.5 μm.
In recent years, it is desired to apply an in-cylinder direct fuel injection device to the combustion engine, particularly, to the gasoline engine for vehicle in order to improve the fuel consumption characteristic, to reduce the amount of harmful exhaust gas and to improve the driving response such as an acceleration performance.
In the fuel pump of the in-cylinder direct fuel injection device, the sliding portions in the pump portion (pressurizing portion) inside the fuel chamber slide on each other under a high surface pressing pressure condition in the fuel (gasoline). Therefore, the portions are considered to be main wearing portions because the portions slide on and contact with each other under a high surface pressing pressure.
In the mechanism portion in the pump portion inside the fuel chamber such as the plunger and the cylinder for pressurizing fuel (gasoline), the sliding between the plunger and the cylinder is performed in the fuel. When gasoline is used as the lubricating oil of the sliding environment, both of the sliding surfaces of the sliding mechanism portions are easily worn because the viscosity of gasoline is extremely small compared to the viscosity of a normal lubricating oil.
In addition, gasoline added with methyl alcohol or methyl alcohol, or degraded gasoline is sometimes used as the fuel. The gasoline of such kind sometimes forms an oxidizing wearing environment. In such a case, the environment to wearing of the contact portions of the sliding mechanism portion becomes severer, and accordingly the wearing amount of the sliding portions is considered to be increased.
When the sliding mechanism portion in the fuel chamber, that is, the contact portions between the cylinder and the plunger reciprocally moving in the cylinder are worn to increase the wearing amount, the suction and delivery efficiency may be decreased, and the reliability may be also decreased.
On the other hand, in the radial plunger pump, a driving cam rotationally moved at a high speed by a transmitted driving force of the engine and a lifter for converting the rotational motion to reciprocal motion slide on each other under an environment of insufficient supply of a lubricating oil (engine oil). Therefore, the seizing resistance and the wear resistance of the driving cam and the lifter from a low speed range to a high speed range are required.
Further, in the rotating slant plate axial plunger pump, the slant plate and the slipper for converting rotation of the shaft to reciprocal motion slide on each other in a lubricating oil (engine oil). Although the sliding is performed in the lubricating oil (engine oil), severe requirement for the properties of the materials may be required depending on the condition of sliding. That is, the seizing resistance and the wear resistance of the members from a low speed range to a high speed range are required.
In other words, there is a problem in that occurrence of abnormal wearing, that is, seizing in the slant plate and the slipper or the driving cam and the lifter of the sliding mechanism portion causes stopping of operation of the fuel pump.
Therefore, each part in the sliding mechanism portion is required durability, particularly, wear resistance and corrosion resistance in fuel having less lubricity, or in a fuel containing an oxidative component, or further in a lubricating oil such as engine oil.
In Japanese Patent Application Laid-Open No. 8-35075, there is description that an ion nitride layer is formed, and a hard layer composed of a nitride, a carbide or a carbonitride of at least one kind selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta and Cr is formed on the ion nitride layer through a PVD method. It is disclosed to apply it to a metal mold in order to improve the adhering property and the durability. However, the seizing resistance, the wear resistance and the corrosion resistance under a high temperature and high surface pressing pressure condition are not discussed.